Class 9 – Concise Physics Selina Solutions
Exercise 1(A) — Multiple Choice Type
1. The condition(s) essential for a unit to be accepted internationally:
Answer: d. All of the above
Reason: The condition(s) essential for a unit to be accepted internationally are:
- The unit should be of convenient size.
- It should be possible to define the unit without any ambiguity.
- The unit should be reproducible.
- The value of the unit should not change with space and time.
2. In mechanics, the three fundamental quantities are:
Answer: d. Length, mass, time
Reason: In mechanics, length, mass and time are the three fundamental units. Unit of length is metre (m), unit of mass is kilogram (kg), unit of time is second (s).
3. How many units are fundamental and complementary?
Answer: c. 7 fundamental, 2 complementary
Reason: Fundamental and complementary units are as follows:
| Fundamental Units | ||
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Temperature | kelvin | K |
| Luminous intensity | candela | cd |
| Electric current | ampere | A |
| Amount of substance | mole | mol |
| Complementary Units | ||
|---|---|---|
| Angle | radian | rd |
| Solid angle | steradian | st-rd |
4. The fundamental unit is —
Answer: d. second
Reason: Out of the given units, only ‘second’ is a fundamental unit.
5. Which of the following unit is not a fundamental unit:
Answer: b. Litre
Reason: Metre, second and kilogram are the fundamental units whereas litre is a derived unit.
6. One millimeter is …………… part of a metre:
Answer: b. One thousandth
Reason: One millimeter is one thousandth part of a metre.
1 mm = 1/1000 m = 10-3 m = 1/10 cm
7. One astronomical unit is equal to:
Answer: a. 1.496 × 1011 metre
Reason: One astronomical unit is equal to the mean distance between the earth and the sun.
1 A.U. = 1.496 × 1011 metre
8. The distance of stars from earth is generally measured in:
Answer: b. Light year
Reason: A light year is the distance travelled by light in vacuum, in one year.
9. 1 Fermi is equal to:
Answer: d. 10-15 m
Reason: Fermi is 10-15th part of a metre. i.e., 1 fermi = 10-15 m
10. The unit of time is:
Answer: c. leap year
Reason: Leap year is the unit of time. Light year, parsec, angstrom are unit of distance. A leap year is the year in which the month of February is of 29 days.
11. 1 Å is equal to:
Answer: a. 0.1 nm
Reason: 10 Å = 1nm
∴ 1 Å = 0.1nm
12. One metric tonne is equal to:
Answer: a. 10 quintal
Reason: It is one thousand times a kilogram. i.e., 1 metric tonne = 1000 kg = 10 quintal.
13. Light-year is the unit of:
Answer: b. Length
Reason: A Light-year is the distance travelled by light in vacuum, in one year.
14. One solar mass is equal to:
Answer: c. 2 × 1030 kg
Reason: The mass of large heavenly bodies is measured in terms of solar mass where 1 solar mass is the mass of the sun i.e., 1 solar mass = 2 × 1030 kg
15. One lunar cycle is nearly equal to:
Answer: b. 29.5 days
Reason: One lunar cycle is the amount of time it takes for the Moon to complete one orbit around the Earth and it is nearly equal to 29.5 days.
16. One shake is equal to:
Answer: b. 10-8 s
Reason: Shake is a smaller unit of time where, 1 shake = 10-8 s and 1 nano shake = 10-9 s
17. Which of the following unit is equivalent to watt?
Answer: a. Volt × Ampere
Reason: watt is the unit of electrical power and is defined as potential × current = volt × ampere.
18. Which one of the following is a derived unit?
Answer: c. Metre3
Reason: Volume is a derived unit. Its formula is:
Volume = length × breadth × height
= metre × metre × metre = metre3
19. The S.I. unit of energy is:
Answer: a. Joule
Reason: Work done or energy = force × displacement = kgm2s-2 or J
20. The S.I. unit of pressure is:
Answer: b. Kg m-1s-2
Reason: Pressure = force/area = Kg m-1s-2
21. Which of the following is the smallest unit?
Answer: c. Fermi
Reason: Fermi is 10-15th part of a metre. i.e., 1 fermi = 10-15 m, hence it is the smallest unit.
Angstrom = 10-10th part of a metre.
Millimetre = 10-3th part of a metre.
Class 9 – Concise Physics Selina Solutions
Exercise 1(A) — Multiple Choice Type
Exercise 1(A) — Very Short Answer Type
Exercise 1(A) — Short Answer Type
Exercise 1(A) — Numericals
Exercise 1(B) — Multiple Choice Type
Exercise 1(B) — Very Short Answer Type
Exercise 1(B) — Short Answer Type
Exercise 1(B) — Long Answer Type
Exercise 1(B) — Numericals
Exercise 1(C) — Multiple Choice Type
Exercise 1(C) — Very Short Answer Type
Exercise 1(C) — Short Answer Type
Exercise 1(C) — Long Answer Type
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